title: Visualization of peripheral nerve degeneration and regeneration: monitoring with diffusion tensor tractography.
abstract: We applied diffusion tensor tractography (DTT), a recently developed MRI technique that reveals the microstructures of tissues based on its ability to monitor the random movements of water molecules, to the visualization of peripheral nerves after injury. The rat sciatic nerve was subjected to contusive injury, and the data obtained from diffusion tensor imaging (DTI) were used to determine the tracks of nerve fibers (DTT). The DTT images obtained using the fractional anisotropy (FA) threshold value of 0.4 clearly revealed the recovery process of the contused nerves. Immediately after the injury, fiber tracking from the designated proximal site could not be continued beyond the lesion epicenter, but the intensity improved thereafter, returning to its pre-injury level by 3 weeks later. We compared the FA value, a parameter computed from the DTT data, with the results of histological and functional examinations of the injured nerves, during recovery. The FA values of the peripheral nerves were more strongly correlated with axon-related (axon density and diameter) than with myelin-related (myelin density and thickness) parameters, supporting the theories that axonal membranes play a major role in anisotropic water diffusion and that myelination can modulate the degree of anisotropy. Moreover, restoration of the FA value at the lesion epicenter was strongly correlated with parameters of motor and sensory functional recovery. These correlations of the FA values with both the histological and functional changes demonstrate the potential usefulness of DTT for evaluating clinical events associated with Wallerian degeneration and the regeneration of peripheral nerves.
authors.affiliation: Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Takagi
authors.forename: Masaya
authors.initials: M
authors.lastname: Nakamura
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamada
authors.forename: Keigo
authors.initials: K
authors.lastname: Hikishima
authors.forename: Suketaka
authors.initials: S
authors.lastname: Momoshima
authors.forename: Kanehiro
authors.initials: K
authors.lastname: Fujiyoshi
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Shibata
authors.forename: Hirotaka James
authors.initials: HJ
authors.lastname: Okano
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Okano
mesh_terms: D000465:Algorithms; D000818:Animals; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D010363:Pattern Recognition, Automated / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012038:Regeneration; D015203:Reproducibility of Results; D012584:Sciatic Nerve / Q000293:injuries* / Q000473:pathology*; D020426:Sciatic Neuropathy / Q000473:pathology*; D012680:Sensitivity and Specificity